[0001] This invention relates to a laminated film structure which is composed of an aromatic
polyester film and an electroconductive metal layer laminated to at least one surface
of the polyester film and which has various improved properties such as superior mechanical
properties, electrical properties, thermal stability, chemical resistance and dimensional
stability.
[0002] More specifically, this invention relates to a laminated film structure composed
of a polyester film and an electroconductive metal layer laminated to at least one
surface of the polyester resin film, characterized in that said polyester film is
an unstretched film of a cured aromatic polyester having a crosslinking degree of
not less than 70%, a swelling degree of not more than 30 and an elongation at room
temperature of not less than 10%; and to a process for producing said film structure.
[0003] Laminated film structures composed of an electrically insulating resin film such
as a stretched (oriented) polyester film, a polyimide film or a glasscloth-epoxy resin
laminated film, and an electroconductive metal layer laminated onto at least one surface
of the film have been used widely in the field of electronics as a flexible circuit,
tape carrier, etc. Polyester films, particularly polyethylene terephthalate films,
have superior mechanical properties and electrical properties, but their thermal stability
is not sufficient. For example, a stretched film of polyethylene terephthalate has
a high shrinkage even at a temperature below its melting point, for example at 230°C,
and its range of application is very much limited. Its chemical resistance and dimensional
stability are inferior to other resins, for example thermosetting resins. A polyimide
film has superior mechanical properties and thermal stability. But its equilibrium
water content is high, and its dimensional stability and electrical properties are
not satisfactory. Moreover, the polyimide film must be formed from a solution, and
this greatly increases its cost. Furthermore, the glasscloth-epoxy resin laminated
film is a thermosetting resin, and has the defect of possessing low elongation and
lacking flexibility.
[0004] The present inventors have made investigations in order to provide a laminated film
structure of an aromatic polyester which can overcome the disadvantages of the aforesaid
conventional laminated film structures, especially laminated aromatic polyester film
structures useful in the field of electronics.
[0005] These investigations have led to the discovery that a laminated polyester film structure
having superior flexibility, a low equilibrium water content, superior electrical
properties and high thermal stability comparable to that of thermosetting resin can
be provided by utilizing an unstretched film of a crosslinked aromatic polyester derived
from a saturated linear aromatic polyester and having the aforesaid properties as
the polyester film layer in the aforesaid film structure.
[0006] It has also been found that such a laminated structure having high delamination strength
can be produced, without the need to interpose an adhesive layer, by providing an
electroconductive metal layer directly on one surface of an unstretched film of an
uncured polyester composed of a saturated linear aromatic polyester containing a photopolymerizable
crosslinking component, and subjecting the resulting structure to the irradiation
of actinic light, preferably ultraviolet light; and that the resulting laminated film
structure of aromatic polyester has moderate elongation and flexibility at room temperature
and feasible strength and dimensional stability at high temperatures.
[0007] The aforesaid cured polyesters and film thereof are disclosed, for example, in German
Laid-Open Patent Publications DOS 2745906 (laid open on April 13, 1978) and DOS 2829572
(laid open on January 11, 1979). Those crosslinked polyesters which are disclosed
in these German Publications and have the properties specified hereinabove can also
be used in the present invention. These German patent documents, however, do not disclose
the utilization of such a film, especially an unstretched film, in metal laminated
film structures for electronics applications, and the excellent improvements achieved
by such film structures.
[0008] It is an object of this invention therefore to provide a laminated film structure
of an aromatic polyester having excellent improved properties which are useful, for
example, in the field of electronics, and a process for its production.
[0009] The above and other objects and advantages of this invention will become more apparent
from the following description.
[0010] The laminated film structure of this invention composed of a polyester film and an
electroconductive metal layer laminated to at least one surface of the polyester film
is characterized in that the polyester film is unstretched, and composed of a cured
aromatic polyester having a crosslinking degree of not less than 70%, a swelling degree
of not more than 30 and an elongation at room temperature of not less than 10%.
[0011] The crosslinking degree, swelling degree and elongation in this invention are determined
by the following methods.
Crosslinking degree
[0012] One hundred milligrams of a crosslinked polyester film is added to 10 ml of a mixture
of phenol and tetrachloroethane in a weight ratio of 60:40, and the mixture is stirred
at 140°C for 30 minutes. Then, the insoluble matter is collected by filtration, washed
with acetone and dried. The amount of the resulting insoluble matter is determined,
and expressed by weight percent based on the crosslinked polyester film. This amount
in percent by weight is defined as the crosslinking degree. Thus, for example, a crosslinking
degree of 70% means that the amount of an insoluble portion in 100 mg of a crosslinked
polyester film is 70 mg.
Swelling degree
[0013] One hundred milligrams of a crosslinked polyester film is allowed to stand at 140°C
for 30 minutes in 10 ml of a mixture of phenol and tetrachloroethane in a weight ratio
of 60:40. Then, the phenol/tetra- chloroethane mixture adhering to the surface of
the film is wiped off, and the weight (W mg) of the film is measured. The film is
washed, and dried, and its weight (G mg) is measured. The swelling degree is calculated
as follows:

Elongation at room temperature
[0014] Measured at room temperature at a stretching speed of 100%/min.
[0015] The cured aromatic polyester film used in this invention has a crosslinking degree
of not less than 70%, a swelling degree of not more than 30, and an elongation at
room temperature of not less than 10%. When the crosslinking degree is less than 70%
or the swelling degree is more than 30, the
' crosslinking of the film is insufficient, and the film has unsuitable thermal stability
for use as a flexible print circuit, etc. If the elongation at room temperature of
the film is less than 10%, its flexibility is not satisfactory. The crosslinking degree
is preferably at least 80%, more preferably at least 85%, especially preferably at
least 90%. The swelling degree is preferably not more than 20, more preferably not
more than 10, especially preferably not more than 5. Furthermore, the above elongation
at room temperature is preferably at least 20%, more preferably at least 30%, especially
preferably at least 50%.
[0016] The cured aromatic polyester film used in this invention has a thickness of preferably
not more than about 1000 microns, more preferably not more than about 500 microns,
especially preferably not more than about 300 microns, and most preferably not more
than about 200 micronso The lower limit of the film thickness is desirably about 10
microns. Preferably, the film has good transparency.
[0017] In a preferred embodiment of this invention, an example of the crosslinked aromatic
polyester is an aromatic polyester cured by irradiation of actinic light, preferably
ultraviolet light, which is composed of (A) a saturated linear aromatic polyester
in which at least 70 mole%, preferably at least 80 mole% , of the acid component consists
of an aromatic dicarboxylic acid or its functional derivative and (B) a photopolymerizable
crosslinking component in an amount of 0.1 to 50 parts by weight per 100 parts by
weight of the saturated linear aromatic polyester.
[0018] In the aforesaid preferred embodiment, examples of the acid component that can be
utilized in forming the saturated linear aromatic polyester (A) include terephthalic
acid, isophthalic acid, naphthalenedicarboxylic acid, diphenyldicarboxylic acid, diphenyl-
sulfonedicarboxylic acid, diphenoxyethanedicarboxylic acid, diphenyletherdicarboxylic
acid, methylterephthalic acid, and methylisophthalic acid. Of these, terephthalic
acid is most preferred.
[0019] Other carboxylic acids may be used in an amount of not more than 30 mole%, preferably
not more than 20 mole%, together with the aromatic dicarboxylic acid as the acid component.
Examples of such carboxylic acids are aliphatic dicarboxylic acids such as succinic
acid, adipic acid, sebacic acid, decanedicarboxylic acid or dodecanedicarboxylic acid;
alicyclic dicarboxylic acids such as hexahydroterephthalic acid; hydroxycarboxylic
acids such as ε-hydroxycaproic acid, hydroxybenzoic acid and hydroxyethoxybenzoic
acid; and ester-forming derivatives of these, such as their lower alkyl esters or
aryl esters.
[0020] Examples of the glycol component of the polyester (A) include ethylene glycol, trimethylene
glycol, tetramethylene glycol, neopentylene glycol, hexamethylene glycol, decamethylene
glycol, cyclohexane dimethylol, 2,2-bis(β-hydroxyethoxyphenyl)propane, hydroquinone,
and 2,2-bis(hydroxyphenyl)propane. Of these, ethylene glycol and tetramethylene glycol
are especially preferredo
[0021] The polyester (A) has an intrinsic viscosity [η], measured at 35°C in o-chlorophenol,
of preferably at least 0.4, more preferably at least 0.5.
[0022] The saturated linear aromatic polyester used in this invention can be produced in
a customary manner by reacting the acid component and glycol component exemplified
hereinabove. This reaction can be performed, for example, at a temperature of about
150 to 320°C at atmospheric pressure in a stream of an inert gas or under reduced
pressure. It is preferred to use a catalyst in this reaction. Examples of suitable
polymerization catalysts are antimony compounds, germanium compounds and titanium
compounds. If desired, the polyester may contain copolymerized therein a monofunctional
compound such as benzoic acid or benzoylbenzoic acid or a polyfunctional compound
such as pentaerythritol, trimethylolpropane, pyromellitic acid or trimellitic acid
in amounts which do not substantially cause a loss of its linearity.
[0023] The photopolymerizable crosslinking component (B) which is included in the saturated
linear aromatic polyester (A) in the aforesaid preferred embodiment by blending and/or
copolymerization is, for example, a compound which has an allyl or substituted allyl
group of the following formula

wherein R
1, R
2 and R
3 are identical or different, and each represents a group selected from the class consisting
of hydrogen, alkyl groups having 1 to 6 carbon atoms, preferably 1 to 3 carbon atoms,
and cycloalkyl groups having 5 to 12 carbon atoms,
said allyl or substituted allyl group being stable under the conditions of forming
a film of the aromatic polyester (A) by melt-shaping, and which optionally contains
at least one ester-forming functional group. Preferred groups of formula (ii) above
include allyl, methallyl and crotyl groups.
[0024] That the allyl or substituted allyl group is stable under the melt-shaping conditions
means that when the above compound is maintained at a temperature at which the polyester
is melted, for example at a temperature 20°C higher than the melting point of the
polyester, in an inert gas for about 15 minutes, the allyl or substituted allyl groups
are present stably without any reaction taking place between these unsaturated groups
or between the unsaturated groups and the polyester.
[0025] Examples of preferred ester-forming functional groups which can be copolymerized
with the aromatic polyester (A) under the melt-shaping conditions for film formation
are epoxy groups of the formula

wherein bonds (f) to (i) are bonded to hydrogen atoms or alkyl groups with 1 to 6
carbon atoms, and bond (i) or bonds (i) and (g) are organic moieties which come within
formula (ii).
[0026] Inclusion of aliphatic unsaturated groups such as allyl or substituted allyl into
the polyester can be achieved by copolymerizing and/or mixing the polyester with the
compound (B) having the aliphatic unsaturated groups. When the compound (B) is to
be copolymerized with the polyester, it should be stable without being decomposed
under the copolymerization conditions, and also contain at least one (preferably two)
ester-forming functional group (e.g., carboxyl, hydroxyl) or groups capable of generating
an ester-forming functional group under the polymerization conditions in addition
to the aforesaid unsaturated groups. Preferably, the latter-mentioned functional group
is, for example, the epoxy group expressed by the above formula. When the compound
(B) is to be incorporated into the polyester, the aliphatic unsaturated groups in
the compound (B) are stable under the conditions of melt-blending with the polyester,
and also the compound (B) itself is desirably stable. Accordingly, when the compound
(B) is to be melt-blended, it is desirable that an insoluble material not soluble
in a mixture of phenol and tetrachloroethane at 35°C should not substantially form
in the resulting composition, and the intrinsic viscosity of the polyester should
not be markedly decreased. Compounds which are decomposed or gasified at the polyester
melting temperature are not desirable in blending with the polyester. From the standpoint
of gasification, compounds having a vapor pressure of not more than 100 mmHg, preferably
not more than 50 mmHg, especially preferably not more than 10 mmg, at the polyester
melting temperature are desirable.
[0027] Those compounds (B) which do not have the aforesaid ester-forming functional group
should desirably contain at least 2, preferably 3 to 4, groups of formula (ii) in
the moleculeo Those compounds (B) which contain the aforesaid ester-forming functional
group should desirably contain at least 1, preferably 2 groups of formula (ii) and
at least 1, preferably 2, ester-forming functional groups.
[0028] Specific examples of preferred photopolymerizable crosslinking compounds (B) are
shown below.
[0029] As compounds having an aliphatic unsaturated group and being capable of blending
with the polyester, those having at least two groups of formula (ii) are preferred
because in the irradiation of actinic light to be described below, they give a firmer
crosslinked structure in the laminated film structure. Examples of such compounds
are given below.
(I) Derivatives of cyanuric acid or isocyanuric acid:-
[0030] Triallyl (or tricrotyl or trimethallyl) isocyanurate, diallyl (or dicrotyl or dimethallyl)
methyl- isocyanurate, diallyl (or dicrotyl or dimethallyl) ethylisocyanurate, ethylenebis(diallyl
(or dicrotyl or dimethallyl) isocyanurate), tetramethylenebis[diallyl (or dicrotyl
or dimethallyl) isocyanurate), hexamethylene- bis(diallyl (or dicrotyl or dimethallyl)
isocyanurate), decamethylenebis(diallyl (or dicrotyl or dimethallyl) isocyanurate),
oxydiethylenebis(diallyl (or dicrotyl or dimethallyl) isocyanurate), triallyl (or
tricrotyl or trimethallyl) cyanurate, diallyl (or dicrotyl or dimethallyl) methylcyanurate,
diallyl (or dicrotyl or dimethallyl) ethylcyanurate, tetramethylenebis(diallyl (or
dicrotyl or dimethallyl) cyanurate), hexamethylene- bis(diallyl (or dicrotyl or dimethallyl)
cyanurate), decamethylenebis(diallyl (or dicrotyl or dimethallyl) cyanurate), and
oxydiethylenebis(diallyl (or dicrotyl or dimethallyl) cyanurate].
[0031] The above compounds can be easily synthesized, for example, by the methods shown
in Zh Organ Khim, 2, (10), pp. 1742-3 (1965) (Russ), or J. Am. Chem. Soc., 73, page
2999 (1951).
(II) Carboxylic acid esters
[0032] Diallyl terephthalate, diallyl isophthalate, diallyl methylterephthalate, diallyl
methylisophthalate, triallyl trimellitate, triallyl trimesate, and tetrallyl pyromellitate.
(III) Compounds having an epoxy group as the ester-forming functional group:-
[0033] Diallyl glycidyl cyanurate, diallyl glycidyl isocyanurate, allyl diglycidyl cyanurate,
allyl diglycidyl isocyanurate; the corresponding cyanuric or isocyanuric acid derivatives
resulting from substitution of a crotyl or methallyl group for the allyl groups in
the above-exemplified compounds; and the corresponding cyanuric or isocyanuric acid
derivatives resulting from substitution of a 2,3-epoxy-2-methylpropyl group, a 2,3-epoxybutyl
group, a 2,3-epoxy-2-methylbutyl group, etc. for the glycidyl groups in the above-exemplified
compounds.
[0034] Among the above compounds having an aliphatic unsaturated groups (polymerizable crosslinking
component (B)), those which can be mixed during the shaping step are preferred. The
compounds exemplified under (I) and (III) above are more preferred, and the compounds
exemplified under (I) above are most preferred.
[0035] The compounds exemplified in German DOS 2745906 and DOS 2829572 can also be used.
[0036] Preferably, the unstretched film of an uncured aromatic polyester composed of (A)
a saturated linear aromatic polyester in which at least 70 mole% of the acid component
consists of an aromatic dicarboxylic acid and (B) a photopolymerizable crosslinking
component in an amount of 0.1 to 50 parts by weight per 100 parts by weight of the
saturated linear aromatic polyester further includes a photo-reaction initiator. Examples
of the photo-reaction initiator are aromatic ketones, benzil, benzil derivatives,
benzoin, benzoin derivatives, and polynuclear quinones. Specific examples of these
compounds are benzophenone, 4-methylbenzophenone, 4-nitrobenzophenone, 3-methylbenzophenone,
4,4'-dimethylbenzophenone, 3,3'-dimethylbenzophenone, 3,4'-dimethylbenzophenone, 4-phenylbenzophenone,
3-phenylbenzophenone, 3,3'-dinitrobenzophenone, 4,4'-dinitrobenzophenone, 3-nitrobenzophenone,
4-methoxybenzophenone, 3-methoxybenzophenone, 4,4'-dimethoxybenzophenone, bis(4-diphenyl)ketone,
bis(3-diphenyl)ketone, 3,4-dimethylbenzophenone, 3,4,3',4'-tetramethylbenzophenone,
Michler's ketone, anthraquinone, nitroanthraquinone, phenanthra- quinone, acetophenone,
propiophenone, benzil, benzoin, benzoin methyl ether, benzoin ethyl ether, benzoin
propyl ether, benzoin butyl ether, benzoin phenyl ether, a-methylbenzoin methyl ether,
a-phenylbenzoin ethyl ether, a-benzylbenzoin ethyl ether, benzil dimethyl ketal, benzil
diethyl ketal, benzil dipropyl ketal, benzil ethylene ketal benzil trimethylene ketal,
benzil neopentylene ketal, benzil bis(2-methoxyethyl)ketal, naphthylphenyl ketone,
bisnaphthyl ketone, ethylenebis-(benzoyl benzamide), tetramethylenebis(benzoyl benzamide),
hexamethylenebis(benzoyl benzamide), decamethylenebis-(benzoyl benzamide), dodecamethylenebis(benzoyl
benzamide), hexamethylenebis(4-acetylbenzamide), hexamethylenebis-[(4-methylbenzoyl)benzamide],
ethylenebis((4-nitrobenzoyl)benzamide), dodecamethylenebis((4-methoxybenzoyl)-benzamide),
dibenzoyl benzene, bis(4-methylbenzoyl)-benzene, ethylenebis(benzoyl phenyl ether),
bis(benzoyl methyl) ether, tris(benzoyl phenoxy)benzene, and bis(4-methoxybenzoyl
methyl ether). Furthermore, those photo-reaction initiators which are described in
German DOS N
os. 1769168, 1769853, 1807297, 1807301, 1919078, and 1949010 and which are substantially
stable under the polyester melting conditions can be used in this invention as desired.
[0037] It is also possible to copolymerize the polyester with benzophenone-4,4'-dicarboxylic
acid. Among the photo-reaction initiators exemplified above, benzil and its derivatives
are preferred. The benzil derivatives are especially preferred because of their high
activity. Furthermore, among the aromatic ketones those having two or more benzophenone
residues are preferred because of their high activity.
[0038] The amount of the photopolymerizable crosslinking component (B) is preferably 0.1
to 50 parts by weight per 100 parts by weight of the aromatic polyester. In particular,
in the case of compounds containing aliphatic unsaturated groups such as allyl or
substituted allyl in the preferred embodiment described hereinabove, the amount may
be about 0.01 to 0.5 equivalent, preferably 0.03 to 0.4 equivalent, especially preferably
about 0.06 to 0.3 equivalent, per 100 g of the polymer. The amount of the photo-reaction
initiator is about 0.01 to 20 parts by weight, preferably 0.05 to 10 parts by weight,
more preferably 0.1 to 5 parts by weight, especially preferably about 0.1 to 3 parts
by weight, per 100 parts by weight of the polyester (A).
[0039] Compounds which contain the aliphatic unsaturated groups mentioned above and have
a photo-reaction initiating action can also be used as the crosslinking component
(B). Examples include N-allyl (or crotyl or methallyl)benzoyl benzamide, N-allyl (or
crotyl or methallyl)anthraquinonecarboxamide, N-allyl (or crotyl or methallyl)benzoyl
phthalimide, N,N-diallyl (or dicrotyl or dimethallyl)benzoyl benzamide, and N,N'-
diallyl (or dicrotyl or dimethallyl)benzophenonetetra- carboxamide.
[0040] The laminated film structure of this invention can be obtained by forming an electroconductive
metal layer on at least one surface of the cured unstretched polyester film obtained
by crosslinking treatment. This can be accomplished by various means. It can also
be obtained by providing. an electroconductive metal layer directly on at least one
surface of an unstretched film of uncured aromatic polyester and subjecting the resulting
structure to irradiation of actinic light such as ultraviolet light
[0041] In any of the embodiments described above, lamination is performed after or while
an unstretched film of uncured polyester composed of the saturated linear aromatic
polyester (A) and the photopolymerizable crosslinking component (B) preferably with
a photo-reaction initiator is formed. For example, a photopolymerizable crosslinking
component having aliphatic unsaturated groups such as allyl or substituted allyl and/or
a photo-reaction initiator may be included in the polyester (A) by copolymerization,
and the mixture, molded into a film form. Or the component (B) and the photo-reaction
initiator may be blended with the polyester (A), and the blend, molded into a film
form.
[0042] In the former embodiment in which the aliphatic unsaturated groups and/or the photo-reaction
initiator are included in the polyester by copolymerization, the polyester-forming
acid component and glycol component, the compound (B) having reactive groups and/or
the photo-reaction initiator are reacted by known polyester-forming means. There can
also be used a master batch method in which a polyester is prepared in advance by
copolymerizing an excess of the aliphatic unsaturated groups and/or the photo-reaction
initiator, and is melt-blended with a polyester not containing the aliphatic unsaturated
groups and/or the photo-reaction initiator.
[0043] In the latter case in which the aliphatic unsaturated groups and/or the photo-reaction
initiator are included into the polyester by blending, the polyester (A), the compound
(B) having aliphatic unsaturated groups and/or the photo-reaction initiator are mixed
by a mechanical mixing means such as an S-type blender or V-type blender. Then, by
using a kneader such as an extruder, the two are blended uniformly at a temperature
at which the polyester is molten or at a higher temperature, preferably at the melting
point of the polyester to a temperature about 60°C higher than the melting point.
[0044] The resulting polyester (A) containing the photopolymerizable crosslinking component
(B) and optionally the photo-reaction initiator is then melted, and continuously formed
into an unstretched film of uncured polyester by usual methods of molding the thermoplastic
resins, such as extrusion molding.
[0045] By subjecting the resulting unstretched film of uncured polyester (A) containing
the photopolymerizable crosslinking component (B) and optionally the photo-reaction
initiator to a crosslinking treatment, there can be obtained an unstretched film of
cured polyester having a crosslinking degree of not less than 70%, a swelling degree
of not more than 30, and an elongation at room temperature of not less than 10%.
[0046] The crosslinking treatment is preferably the irradiation of actinic light such as
ultraviolet light, electron beams and radioactive rays. The use of ultraviolet light
is especially preferred.
[0047] Ultraviolet light is irradiated at room temperature to a temperature lower than the
decomposition temperature of the polyester (A), preferably from the second order transition
point (Tg) to the melting point (T ) of the polyester (A), more preferably from (Tg
+ 10) to T
m (°C), especially preferably from (Tg + 10) to (T - 10) for a period of 1 second to
10 hours, preferably 2 seconds to 1 hour, more preferably 5 seconds to 30 minutes,
particularly preferably from 10 seconds to 10 minutes.
[0048] Reinforcing materials such as glass fibers, mica or talc may be included in the crosslinked
polyester film used in this invention. This can be easily achieved, for examples,
by mixing a reinforcing material as well as the crosslinking component (B) and optionally
the photo- , reaction initiator with the polyester (A), melt-extruding the mixture,
and then subjecting the product to the aforesaid crosslinking treatment. It is also
possible to melt and impregnate the polyester (A) containing the crosslinking component
(B) and optionally the photo-reaction initiator in a glass cloth, and subjecting the
impregnated glass cloth to the crosslinking treatment. This affords a crosslinked
polyester film having superior dimensional stability and thermal stability.
[0049] The laminated film structure of this invention can be obtained by forming an electroconductive
metal layer on at least one surface of the unstretched film of cured polyester which
can be obtained in the aforesaid manner. Or it may be formed by providing an electroconductive
metal layer directly on at least one surface of the unstretched film of uncured polyester
before the crosslinking treatment, and subjecting the resulting assembly to the crosslinking
treatment.
[0050] The former embodiment of forming the electroconductive metal layer can be performed
by various means which can be roughly classified into a type in which an electroconductive
metal foil is bonded to the crosslinked polyester film through an adhesive layer,
and a type in which an electroconductive metal layer is deposited on the cured polyester
film by electroless plating.
[0051] Copper, aluminum, etc. are used as the electroconductive metal layer. A copper foil
is especially preferred. The copper foil includes both an electrolytic copper foil
and a rolled copper foil, and generally the electrolytic copper foil is used. The
rolled copper foil is preferred when flexibility is required. When the adhesive is
used, it is preferred to use a surface- oxidized copper foil having good adhesiveness.
It is also possible to use a combination of electroless plating and electroplating
in the formation of an electroconductive metal layer, especially a copper layer, on
the cured polyester film.
[0052] The method of lamination by bonding is used widely, and can be used also in preparing
the laminated film structure of this invention. Preferred adhesives are those which
have good adhesion to the cured polyester film and the electroconductive metal foil
and have superior electrical properties and thermal stability. Adhesives generally
used for polyesters can be directly applied to the preparation of the laminate film
stricture of this invention. Preferred examples are urethane-modified polyester-type
adhesives, and polyester-modified epoxy-type adhesives. The urethane-modified ester-type
adhesives are particularly preferred.
[0053] The bonding can be performed, for example, by continuously applying a solution of
such an adhesive to the cured polyester film by coating means such as a roll coater,
heating the coated film to remove the solvent, and pressing the conductive metal foil
against the coated surface by a hot roller. For example, the cured polyester film
and the conductive metal foil are bonded preferably under the following conditions
of laminating temperature T
L (°C) and laminating pressure G (kg/cm
2).


[0054] In the above expressions, Tp is the temperature at which the viscosity of the adhesive
is at least 10 poises but below 1000 poises; P is the viscosity of the adhesive at
temperature Tp; and ℓnP is the natural logarithm of P.
[0055] The laminate film structure of this invention can be produced with commercial advantage
by the above method.
[0056] The laminate film structure can also be produced by forming the conductive metal
layer by electroless plating. For example, a copper layer can be formed on the cured
polyester film by activating the surface of the cured polyester film by a known method,
and then dipping the film in an electroless copper plating bath. A copper layer having
a thickness of less than about 10 microns can be formed by electroless plating alone.
If a thickner copper layer is required, electroplating is performed to the desired
thickness after the electroless plating. In order to increase the adhesion of the
polyester film to the copper foil, it is preferred to perform soft etching, such as
treatment with amines, on the film.
[0057] According to the latter-mentioned embodiment of forming the electroconductive metal
layer, it is possible to provide the electroconductive metal layer directly on at
least one surface of the unstretched film of uncured polyester and then subjecting
the resulting structure to crosslinking treatment.
[0058] According to this embodiment, the conductive metal foil is bonded to the unstretched
film of uncured polyester film containing the crosslinking component (B) by coating
means such as a hot press roller or laminator, and then to subject the resulting structure
to crosslinking treatment as described above. Association of the base polyester film
and the electroconductive metal foil can be achieved after the molding of the unstretched
polyester film and before the crosslinking treatment of the polyester film. For example,
there can be used a so-called extrusion laminating method which comprises laminating
the metal foil to the polyester film during the melt-extrusion of the polyester, and
a method which comprises melt-extruding the polyester into a film and bonding the
metal foil and the film with a hot press roller.
[0059] In the extrusion laminating method, in order to increase the adhesion between the
polyester layer and the metal layer, it is preferred to perform bonding with a hot
press roller when the temperature of the polyester reached a predetermined point described
hereinbelow after the polyester has been cast on the metal foil.
[0060] Preferably, the temperature (TH, °C) at which the metal foil and the unstretched
film of the uncured polyester with a hot press roller should be within the range specified
by the following equations depending upon the weight percent (W) of the photopolymerizable
crosslinking component (B).


[0061] The bonding pressure is at least 2 kg/cm
2, preferably at least 3 kg/cm
2 and especially preferably at least 5 kg/cm
2 but does not exceed 250 kg/cm
2, preferably 150 kg/cm
2, especially preferably 100 kg/cm
2. The time required for bonding with a roller is at least about 0.5 second, preferably
at least about 1 second. The bonding conditions are desirably varied depending upon
the material of the surface of the roll within the above- specified conditions. The
material of which the surface of the roll is made affects the appearance of the outside
surface of the polyester film layer of the laminate film structure obtained by bonding.
Such a material should withstand continuous long-term use at the bonding temperature
TH. For example, it may be a hard-plated polished roll, a silicone rubber-lined roll,
or a Teflon-lined roll.
[0062] A multiplicity of roller units at different heating temperatures and pressures may
be used in order to perform the heat bonding of the laminate film structure more effectively.
[0063] The laminate film structure of this invention can be produced by irradiating actinic
light, preferably ultraviolet light, onto the polyester layer of the laminated structure
to cure the polyester.
[0064] According to this invention, the firm bonding between the electroconductive metal
layer and the unstretched polyester film layer and the curing of the polyester can
be performed simultaneously by the aforesaid embodiment in which the adhesive layer
is not used. The conditions for ultraviolet radiation may be the same as those used
in the first-mentioned embodiment in which the adhesive layer is used.
[0065] The laminated polyester film structure obtained by the above bonding and crosslinking
treatment can be used directly. The adhesion between the layers can be further increased
by heat-treating the resulting laminate film structure at a temperature of at least
about 150°C, preferably at least about 180°C, more preferably at least about 210°C,
for at least about 10 seconds, preferably at least about 30 seconds, more preferably
at least about 1 minute but not exceeding 60 minutes, preferably about 30 minutes.
This heat-treatment may be carried out in hot air. To inhibit oxidation of the bonded
metal foil, however, it is convenient to apply infrared heating from the side of the
polymer layer of the laminated film structure.
[0066] If desired, a glass cloth layer may be provided on that surface of the laminated
film structure of this invention which is opposite to the surface having the electroconductive
metal layer. In the performance of this embodiment, the uncured polyester film containing
the crosslinking component (B), a glass cloth and an electroconductive metal foil
are bonded by a hot press roller, a laminator, etc., and the polyester in the resulting
laminated structure is cured by irradiation of actinic light, particularly ultraviolet
light.
[0067] The sequence of lamination of the individual layers is, for example, such that the
electroconductive metal foil (M), the unstretched film of uncured polyester (P) and
the glass cloth (G) are arranged in this order (M.P.G. arrangement), or a four layer
structure of M.P.G.P. in this order is provided. A preferred method of lamination,
for example, comprises melt-extruding the polyester from a shaping die having a predetermined
clearance, and while the film is not fully cooled, laminating the metal foil to one
surface of the unstretched polyester film and the glass cloth to the other surface
(the extrusion-laminating method); or first forming the unstretched film of uncured
polyester, and then bonding the glass cloth to one surface of the film and the metal
foil to the other by using a hot press roller.
[0068] In the above extrusion-laminating method, too, it is recommended for increased adhesion
between the unstretched film of uncured polyester and the metal or glass cloth that
the bonding with a hot press roller should be carried out when the temperature of
the polyester reaches the predetermined temperature point specified hereinabove. When
the lamination is performed by the M.P.G.P. four-layer method, it is preferred to
bond a composite film structure of M.P.G. to the unstretched film of uncured polyester
film (P), or a laminate film of M.P. to a laminate film of G.P., using a hot press
roller. Also, when the unstretched film of uncured polyester is first formed and then
the conductive metal foil (M) or glass cloth (G) is laminated thereto by means of
a hot press roller, it does not matter whether the required layers are laminated in
the predetermined sequence and bonded at a time, or they are laminated and bonded
one by one. To perform lamination economically on an industrial scale, however, it
is advantageous to bond all the required layers at a time.
[0069] In the bonding of the polyester film, glass cloth and conductive metal foil by a
hot press roller, the temperature (TH), the pressure, the type of roll used, etc.
may be the same as those described with regard to the first-mentioned embodiment.
[0070] The conditions for curing the uncured polyester in the structure by ultraviolet irradiation,
and for heat-treatment may be the same as those described hereinabove with regard
to the aforesaid embodiment.
[0071] The laminated film structure of this invention composed of an unstretched film of
cured polyester having a crosslinking degree of not less than 70%, a swelling degree
of not more than 30 and an elongation at room temperature of not less than 10% and
an electroconductive metal layer laminated to at least one surface of the polyester
film has superior thermal stability and dimensional stability, and can, for example,
be soldered at a temperature of more than about 260°C, and even more than about 300°C.
The adhesion between the unstretched cured polyester film layer and the metal layer
is high, and the delamination strength is at least 1 kg/cm, especially at least 1.5
kg/cm.
[0072] The electroconductive laminated film structure of this invention can be utilized
in materials which require both thermal stability and flexibility, such as flexible
print circuits, tape carriers and panel heaters.
[0073] The following examples further illustrate the present invention. All parts in these
examples are by weight. The intrinsic viscosity of polymer is measured at 35°C in
o-chlorophenol. The flexural strength is evaluated by bending a sample at a radius
of curvature of 0.4 mm and observing the bended state with the naked eye.
Examples 1 to 3 and Comparative Example 1
[0074] One hundred parts of polyethylene terephthalate (intrinsic viscosity 0.65) having
copolymerized therewith 15%, based on the total glycol component, of cyclohexane-1,4-dimethanol
was well blended by an S-type blender with the crosslinking agents and photo-reaction
initiators shown in Table 1 in the amounts indicated. The mixture was melt-extruded
from a T-die to form a transparent amorphous film having a thickness of about 100
microns. The film was exposed to light from a 2KW high-pressure mercury lamp (30 W/cm)
at a distance of 20 cm at 130°C for 3 minutes to form a cured polyester film.
[0075] The film was degreased with acetone, and an adhesive having the following composition
was coated on one surface of the film by a bar coater (No. 20).
Composition of the adhesive
[0076]

The coated film was treated at 170°C for 5 minutes to remove the toluene. An electrolytic
copper foil having a thickness of 35 microns was applied to the cured film and the
assembly was heat-bonded between two hot rollers kept at 150°C. The resulting structure
was further heat-treated at 170°C for 10 minutes to cure the adhesive layer. The crosslinking
degree, swelling degree and elongation at room temperature of the cured film, the
thermal stability of the laminated film structure, and the delamination strength of
the copper foil are shown in Table 1.

[0077] Table 1 also shows the results obtained with a laminate film comprising a biaxially
stretched film of polyethylene terephthalate for comparison.
[0078] It is seen from Table 1 that the laminated film structures of this invention have
superior solder resistance because of the use of the highly cured polyester film,
and good flexibility because of having a sufficient elongation.
Example 4
[0079] One hundred parts of polybutylene terephthalate having an intrinsic viscosity of
0.70 was mixed well by an S-type blender with 20 parts of ethylene- bis(diallyl isocyanurate)
as a crosslinking agent and 1 part of benzil dimethyl ketal as a photo-reaction initiator.
The mixture was melt-extruded from a T-die, and quenched to obtain a transparent film
having a thickness of 120 microns. The film was subjected to the irradiation of light
from a 2KW high-pressure mercury lamp (30 W/cm) at a distance of 10 cm at 150°C for
2 minutes to form a cured film. The cured film was degreased with acetone, and an
adhesive having the following composition was coated on one surface of the film by
a bar coater (No. 20).
Composition of the adhesive
[0080]

The coated film was heat-treated at 170°C for 5 minutes, and a surface oxidized copper
foil having a thickness of 35 microns was heat-bonded with the film at 170°C. The
crosslinked film of polybutylene terephthalate used as a base film had a crosslinking
degree of 98%, a swelling degree of 1, and an elongation at room temperature of 30%.
The delamination strength in the 180° direction of the copper foil was 1.5 kg/cm,
and the solder resistance (260°C, 30 seconds) of the laminate film was good with no
change observed. When the resulting laminate structure was dipped in trichloroethylene
for 5 minutes, no change was observed.
Example 5
[0081] One hundred parts of polyethylene terephthalate (intrinsic viscosity 0.78) having
copolymerized therewith 15%, based on the total acid component, of isophthalic acid
and 30%, based on the total glycol component, of neopentylene glycol was blended well
by an S-type blender with 5 parts of diallyl glycidyl isocyanurate and 15 parts of
hexamethylenebis(diallyl isocyanurate) as a crosslinking agent and 2 parts of benzil
ethylene ketal as a photo-reaction initiator. The mixture was melt-extruded from a
T-die to form a transparent amorphous film having a thickness of about 50 microns.
The resulting film was subjected to the irradiation of light from a 2KW high-pressure
mercury lamp at 130°C for 5 minutes to form a cured film having a crosslinking degree
of 88%, a swelling degree of 3.5 and an elongation at room temperature of 120%. The
cured film was dipped for 1 minute in a 50% aqueous solution of monoethylamine, washed
with water, dried, and then degreased with acetone. An adhesive having the following
composition was coated on the film by a bar coater (No. 20).
Composition of the adhesive
[0082]

The coated film was dried at 170°C for 5 minutes, and an electrolytic copper foil
having a thickness of 35 microns was heat-bonded et 150°C. The delamination strength
of the copper foil was 1.8 kg/cm, and no change was noted in the laminated film structure
in a solder resistance test conducted at 260°C for 30 seconds. When the film was dipped
in acetone or trichloroethylene for 5 minutes, no change was noted in the film. The
laminated film structure also had good flexibility.
Example 6
[0083] Polybutylene terephthalate (intrinsic viscosity 0.70) was melted in an extruder,
and a mixture of triallyl cyanurate and benzophenone (weight ratio 6:1) as a crosslinking
agent was introduced into the extruder from a side pipe provided therein for blending
of the crosslinking agent. Thus, the polybutylene terephthalate was mixed in the extruder
with triallyl cyanurate and benzophenone. The mixture was extruded from a T-die, and
quenched to afford a transparent film having a thickness of about 100 microns. The
film was then subjected to the irradiation of light from a 2KW high-pressure mercury
lamp (30 W/cm) at a distance of 20 cm at 130°C for 5 minutes to form a cured film
having a crosslinking degree of 95%, a swelling degree of 1.5 and an elongation at
room temperature of 50%. The cured film was dipped for 1 minute in a 50% aqueous solution
of monoethylamine at room temperature, and washed with water. The film was further
dipped for 10 minutes in HS-101B (a sensitizer for electroless copper plating, a product
of Hitachi Chemical Co., Ltd.), and washed with water. Furthermore, it was dipped
for 5 minutes in ADP-201 (a bonding promoter, a product of Hitachi Chemical Co., Ltd.)
and washed with water. Subsequently, the film was dipped at 25
0C for 15 minutes in an electroless copper plating bath (CUST-201), washed with water,
and then subjected to copper electroplating using a copper sulfate bath. There was
obtained a laminate film copper-clad on both surfaces and having a copper layer thickness
of about 30 microns. In the laminated film, the delamination strength in the 180°
direction of the copper layer was 0.9 kg/cm. When it was subjected to a solder resistance
test at 260°C for 30 seconds, no change was noted in the laminated film. Examples
7 to 10
[0084] Polyethylene terephthalate (intrinsic viscosity 0.74) having copolymerized therewith
15 mole%, based on the total acid component, of isophthalic acid was fully dried,
and metered and fed into a vent-equipped extruder having two screws of 30 mm in diameter
adapted to rotate in different directions. The polymer was thus melted within the
cylinders. The crosslinking agent and photo-reaction initiator shown in Table 2 were
fed into the extruder from the vent portion using a metering pump. The molten polymer
was intimately blended with these additives, and the uniform intimate blend was conducted
to a T-die, and extruded onto a cooled drum to form a transparent amorphous film having
a thickness of about 100 microns. The film and a copper foil (for use in a print circuit
board) having a thickness of 35 microns and not coated with an adhesive were bonded
by two hot rollers lined with a silicone rubber under the bonding conditions shown
in Table 2. The polyester film layer was subjected to irradiation of ultraviolet light
from a 2KW high-pressure mercury lamp (20 W/cm) at a distance of 20 cm for 3 minutes
to cure it, and then heat-treated at each of the temperatures shown in Table 2. The
resulting laminated film structure was tested for delamination strength, and also
subjected to a solder resistance test at 260°C for 30 seconds. The results are shown
in Table 2.
Examples 11 and 12
[0085] Polyethylene terephthalate (intrinsic viscosity 0.72) having copolymerized therewith
15 mole%, based on the total acid component, of isophthalic acid and 20 mole%, based
on the total glycol component, of neopentylene glycol was blended with the crosslinking
agent and photo-reaction initiator shown in Table 2 and formed into a film in the
same way as in Example 7.
[0086] Laminated film structures were prepared from the resulting films in the same way
as in Example 7. The laminated film structures were tested for delamination strength,
and also subjected to a solder resistance test at 260°C for 30 seconds. The results
are shown in Table 2.
Comparative Examples 2 and 3
[0087] An attempt was made to bond a copper foil to a film obtained by the same procedure
as in Example 7 or Example 11 except that the crosslinking agent and photo-reaction
initiator were not added to the polymer of Example 7 (Comparative Example 2) or the
polymer of Example 11 (Comparative Example 3). The copper foil scarcely adhered to
the film.

Examples 13 to 16
[0088] Polyethylene terephthalate (intrinsic viscosity 0.74) having 15 mole%, based on the
total acid component, of isophthalic acid copolymerized therewith was fully dried,
and then metered and fed into a vent-equipped extruder having two screws of 30 mm
in diameter adapted to rotate in different directions. Thus, the polymer was melted
in the cylinder, and each of the crosslinking agents and each of the photo-reaction
initiators shown in Table 3 were introduced into the extruder by means of a metering
pump. The polymer and the additives were blended intimately, and the intimate uniform
blend was conducted to a T-die and extruded onto a cooled drum to form a transparent
amorphous film having a thickness of about 100 micrnns.
[0089] The resulting film (P), a commercially available plain-weave glass cloth (G) having
a thickness of 30 microns, and a copper foil (M) (for use in a print circuit board)
having a thickness of 35 microns and not coated with an adhesive were bonded by using
two hot rollers lined with a silicone rubber under the bonding conditions shown in
Table 3. The polyester layer was then subjected to irradiation of ultraviolet light
from a 2KW high-pressure mercury lamp (30 W/cm) at a distance of 20 cm for 3 minutes
to cure it, .and, then heat-treated at each of the temperatures shown in Table 3 to
form an electroconductive composite film. The composite film was tested for delamination
strength and subjected to a solder resistance test at 260°C for 30 seconds.
[0090] Two markers with a distance of about 10 cm from each other were provided in the composite
film, and the distance between the markers was measured after the solder resistance
test. Dimensional changes (%) were determined from the results of measurement.
[0091] The flexural resistance of the resulting composite film structure was examined by
bending the film sample, holding it with fingers to maintain a bended state, and then
returning it to the original state.
[0092] The results are shown in Table 3.
Examples 17 and 18
[0093] Polyethylene terephthalate (intrinsic viscosity 0.72) having 15 mole%, based on the
total acid component, of isophthalic acid and 20 mole%, based on the total glycol
component, of neopentylene glycol copolymerized therewith was blended with each of
the crosslinking agents and each of the photo-reaction initiators shown in Table 3
and formed into a film in the same way as in Example 13.
[0094] Electroconductive laminated film structures were prepared from the resulting films
in the same way as in Example 13. The delamination strengths and solder resistancesof
these film structures were determined. The results are shown in Table 3.
Comparative Examples 4 and 5